Internal combustion engines may include water injection systems that inject water into a plurality of locations, such as into an intake manifold, upstream of engine cylinders, or directly into engine cylinders. Engine water injection provides various benefits such as an increase in fuel economy and engine performance, as well as a decrease in engine emissions. In particular, when water is injected into the engine intake or cylinders, heat is transferred from the intake air and/or engine components to the water, leading to charge cooling. Injecting water into the intake air (e.g., in the intake manifold) lowers both the intake air temperature and a temperature of combustion at the engine cylinders. By cooling the intake air charge, a knock tendency may be decreased without enriching the combustion air-fuel ratio. This may also allow for a higher compression ratio, advanced ignition timing, improved wide-open throttle performance, and decreased exhaust temperature. As a result, fuel efficiency is increased. Additionally, greater volumetric efficiency may lead to increased torque. Furthermore, lowered combustion temperature with water injection may reduce NOx emissions, while a more efficient fuel mixture (reduced enrichment) may reduce carbon monoxide and hydrocarbon emissions.
Water injection systems include a water reservoir which may be refilled manually as well as opportunistically via water generated on-board the vehicle. For example, water in the form of condensate may be retrieved from one or more components, such as an EGR cooler, an AC evaporator, an exhaust heat exchanger, a charge air cooler, a vehicle external surface, etc. However, based on the source of the water, the quality of water injected into the engine may vary. In particular, the nature of contaminants present in the water, as well as the degree of contamination, may vary widely based on where the vehicle operator refilled the water tank from. For example, it may be recommended to refill the water tank with distilled water, but the operator may refill with tap water or well water instead. This variation can result in minerals getting deposited on water filters, water injectors, engine parts, exhaust catalysts, etc., affecting engine performance as well as potentially damaging engine hardware.
Various approaches have been developed to test the quality of water available on-board a vehicle water injection system. For example, a variety of dedicated water quality sensors may be provided, such as conductivity sensors, turbidity sensors, pH sensors, etc. However, the addition of dedicated sensors for water quality assessment may add to engine costs. Further, engine controls may need to be modified to periodically diagnose the sensors. Furthermore, a variety of sensors may be required to accurately assess the water quality since the nature of contaminants present in the water may vary widely. Reliance on a single type of sensor to determine if the available water is of poor quality may be error prone.
In one example, some of the above issues may be at least partly addressed by a method for an engine in a vehicle, comprising: injecting an amount of water from a water reservoir into an engine; comparing a first estimate of the water injection amount based on a change in manifold charge temperature to a second estimate of the water injection amount based on a change in intake oxygen level; and adjusting a subsequent water injection to the engine based on the comparing. In this way, the quality of the injected water may be assessed and water injection may be adjusted in accordance.
As an example, an engine may be configured with a water injection system that enables water to be injected into one or more engine locations, such as into an intake manifold. The water injection system may include a water injector as well as a water reservoir supplying water to the injector. The water reservoir may be manually refilled by a vehicle operator. Additionally, the water reservoir may be coupled to a water collection system that opportunistically refills the reservoir with water generated on-board the vehicle. For example, water in the form of condensate may be retrieved from one or more engine components, such as an EGR cooler, an AC evaporator, an exhaust heat exchanger, a charge air cooler, a vehicle external surface, etc. Based on engine operating conditions, an amount of water may be delivered into the engine intake manifold. A controller may infer an actual amount of water delivered into the engine based on a change in manifold charge temperature (MCT) following the injecting. In addition, the controller may infer the actual amount of water dispersed into the engine (that is, the portion of the injection that provides the actual charge cooling effect) based on a change in intake dilution level (or intake oxygen level). As such, a discrepancy between the amount of water injected and the amount of water dispersed (or vaporized) may be due to the quality of the water. In particular, as the quality of water decreases, a smaller portion of the injected water may vaporize. Consequently, the contaminants may reduce the effectiveness of the water injection. As one example, as the salt or ion content of the water increases, the boiling temperature of the water solution may rise, resulting in a smaller portion of water evaporating and dispersing into the intake aircharge at a given aircharge temperature. Thus, the controller may correlate water quality with a water injection error learned based on a difference between the change in MCT relative to the change in intake oxygen level following the water injection. During a subsequent water injection event, the commanded injection amount may be adjusted with a correction factor that compensates for the learned water injection error. In addition, if the water quality is deemed poor (such as when the water quality is lower than a threshold), water usage may be adjusted, such as by increasing water usage in a defined operating window so as to expedite water refilling.
In this way, a water quality can be reliably assessed using existing sensors. The technical effect of learning a water injection error based on distinct sets of engine operating parameters at the same engine operating condition, following a given water injection, is that even small differences between the water that is injected and the water that has vaporized can be reliably measured using sensors already present in the system. As a result, the water injection error may be robustly determined without reliance on expensive and dedicated water quality sensors, and water injection can be adjusted accordingly. In addition, by correlating the errors in water injection amount a water quality, the water quality may be reliably assessed, reducing system damage from contaminated water. Further, by adjusting water usage based on assessed water quality, parasitic losses and financial costs of purifying the water are minimized. The technical effect of integrating the water injection system with a control system that protects against contaminated water usage is that continued refilling of a water reservoir with contaminated water is reduced, extending engine component life. By improving water usage, the benefits of water injection can be extended.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.